1. Field of the Invention
This invention is directed to a micro-electrical discharge machine (μEDM) based metrology system using a styli and sensing at pica joule energy levels. The micro-electrical discharge machine based metrology system is a non-contact, non-destructive, and on-board metrology system capable of in-process quality assurance/quality control (QA/QC).
2. Discussion of Related Art
Many industries, including semiconductor, medical, automotive, defense and aerospace have an increasing need for parts with dimensions measured in microns, commonly known as microstructures. However, known methods for measuring these microstructures have various short-comings which often result in the need to scrap parts which are manufactured out of specification.
When a conventionally-sized part is manufactured, the part can be removed from the machining platform and measured. If a dimension is found to be out of tolerance, the part can be placed back onto the machining platform for additional work. However, as machined parts are reduced in size to microns with even smaller tolerances, it is impractical for these parts to be re-positioned on the machine after measuring with the necessary accuracy. Accordingly, in order to maintain reference points on the machined part, the part must be measured on the machining platform prior to removal. If a part is removed from the machine to be measured and found to be out of specification, the part must be scrapped as it is very difficult to reposition in the machine with the accuracy necessary for additional machining. The machining process must then be modified and a new part fabricated. This costs time, money, and results in material waste.
Known on-machine metrology devices can cut this drop-out rate by 90%, resulting in substantial savings to the manufacturer, supplier, and consumer. However, these known metrology platforms are expensive, have fragile sensors and have a limited scope of measurement.
Known on-machine micro-metrology systems are generally divided into two types, tactile or optical systems. Optical systems, either visible or laser, are limited by line-of-sight restrictions (if it can't see it, it can't measure it). While tactile based systems have delicate sensors with limited ranges with respect to aspect ratios, sidewalls, and overhangs. Tactile sensors also rely on surface contact with the part, surface contact can leave witness marks, scratches or blemishes that can render a part unusable for an intended purpose. As an example, one type of ultra-high precision probe will contact a surface with 0.300 Nm/μm of force. This force is 15 billion times greater than the smallest force from the sensor of this invention.
Both tactile and optical systems are also adversely affected by machine oils and other machining residues. For either of these systems to be effective, additional cleaning steps are necessary both inside and outside of the machining platform prior to use.
As such, there is a need for an improved metrology system for measuring micro-sized components that avoids the short-comings of known metrology systems.